Given the increasing level of threat in the current climate, the use of X-ray imaging for inspecting all types of baggage and cargo is increasing. Although there is a benefit associated with X-ray scanning, there is also a detriment due to radiation dose to the object being inspected, to the operators of the radiation-producing scanning equipment, and to members of the public in the vicinity of the scanning equipment during operation. A good X-ray scanning system design shall seek to optimise image quality in order to provide a sufficient level of detection capability while simultaneously seeking to minimise the overall radiation dose that is delivered during scanning
Currently known systems are generally designed in such a way that a single optimisation condition is used for all imaging, and this condition is generally the one which achieves maximum penetration performance, best spatial resolution and best contrast performance simultaneously for a given radiation footprint. Generally, penetration performance is optimised by selecting the energy of the X-ray source, spatial resolution is optimised by selecting the granularity of the X-ray detector, and contrast performance and penetration performance are optimised together through X-ray source output dose rate. Typically, collimation is used to provide a fan beam of radiation to constrain the X-ray beam to a narrow volume that extends from the X-ray source to cover some or all of the detection elements. This collimation acts to reduce X-ray scatter, and to further influence penetration, contrast performance and overall delivered radiation dose. The radiation footprint is determined by the maximum source output that delivers a regulatory dose to the public in the desired perimeter.